Thermal expansion and conductivity of magnetite flakes taken from the Oconee-2 steam generator

Flakes consisting primarily of iron oxides (magnetite) have been discovered in the spaces between tubes and support plates in steam generators, increasing flow resistance and causing abnormal increases in water levels. To aid in the determination of the effects of tube scale on steam generators, Duke Power Company and MPR Associates, Inc. arranged for the author to measure the thermal expansion and thermal conductivity of tube scale specimens from the steam generator of the Oconee-2 pressurized water reactor. The study measured the thermal expansion of the flakes directly, using miniaturized specimens, rather than deriving these data from X-ray powder diffractometry as in past studies.The flakes are composed of multiple layers, each of which exhibits different thermal behaviour. Thermal expansion was higher than that for Fe₃O₄. The average thermal conductivity for two- and three-layered flakes is 0.026 J sec^–1 cm^–1 ° C^–1. The thermal conductivity for a singlelayered flake is 0.060 J sec^–1 cm^–1 ° C^–1.The work was performed during employment at Battelle.